From swillett@igc.apc.org Thu Oct 12 10:26:34 1995
To: loeb@psyche.mit.edu
Subject: Re: Cambridge PR Voting Demo
Cc: jlindsay@netcom.com
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> From loeb@psyche.mit.edu Tue Oct 3 13:23:18 1995
> Date: Tue, 3 Oct 95 16:23:31 EDT
> From: Eric Loeb
> To: swillett@igc.apc.org
> Subject: Re: Cambridge PR Voting Demo
>
> I mailed you the code. Let me know if you have any questions
> or comments. It was hacked together rather quickly...
>
> eri
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Thanks, Eric, for sending me your code for this demonstration. I
appreciate the effort you have put in on this demonstration, since I
know from my own experiences that people can get really confused trying
to figure out how PR systems work! Anything which gives them an
example helps make the process more real.
My concern is that I don't think your demo correctly implements voting
the way the Cambridge rules require. I don't claim to be an expert on
the Cambridge election code, but I talked to Jim Lindsay, who authored
PRMaster, a PR vote processing program (which successfully duplicated
the count of Cambridge's last election) and we are concerned with the
way you have handled resolving a tie.
One of the key features of STV voting (the single transferrable vote
method which Cambridge uses) is that additional (lower) preferences a
voter expresses can in no way adversely affect a candidate they prefer
more. If, however, you tally second choice ballots while the fate of
first choice candidates is still undetermined then someone's second
choice could knock out their first choice candidate!
This implies that you MUST resolve ties if there are no more surplus
votes to be transferred and the election is not yet resolved before you
can proceed to count second (or third, etc.) preferences. I think
Cambridge does this randomly (select one of the tied lowest
vote-getters and eliminate them). Then the votes of that candidate are
transferred to the next candidate ON THOSE BALLOTS. You do not count
ALL the second (or third, etc.) choice votes, just the next choice on
the ballots which have been "released" by eliminating their current top
choice.
I hope this makes some sense. I would be happy to continue to discuss
these rules and, if I am incorrect, I hope you will let me know.
Once again, I appreciate the time you have spent trying to work out
this demo!
Steve Willett